1. Field of the Invention
The present invention relates to a fuel reforming apparatus for reforming a hydrocarbon-based fuel to produce a hydrogen-rich gas.
2. Description of the Related Art
Hydrogen-rich gas is producible by reforming hydrocarbon-based fuel. The hydrocarbon-based fuel can be natural gas primarily containing methane, an alcohol such as methanol, gasoline, or the like. The reforming catalyst and reforming reaction temperature are appropriately selected in accordance with the starting material fuel used when the hydrogen-rich gas is produced by the reforming reaction. The hydrogen-rich gas thus produced may, for example, be fed to fuel cells and used as fuel gas when electromotive force is to be created by an electrochemical reaction.
JP 11-79703A discloses a reforming apparatus in which gasoline is used as the reforming fuel, and a partial oxidation reaction is performed together with the steam reforming reaction in a water gas reforming reactor to produce a hydrogen-rich gas. A significant advantage of gasoline is that it is widely available as a commercial fuel for producing hydrogen-rich gas.
Using gasoline or another higher hydrocarbon-based fuel as a reforming reaction fuel is disadvantageous, however, in that soot tends to form in the reforming reactor. The soot gradually reduces the activity of the reforming reaction by covering the surface of the reforming catalyst within the reforming reactor. It is therefore desirable that soot formation be reduced and the activity of the reforming reaction be prevented from being reduced due to the soot coating on the reforming catalyst when gasoline or another higher hydrocarbon-based fuel is used as the reforming reaction fuel.
Another disadvantage of using gasoline or a similar higher hydrocarbon-based fuel for a reforming reaction is that this reaction is more difficult to perform in an adequate manner and that more fuel is likely to remain unreacted than when methanol, methane (natural gas), or another known hydrocarbon-based fuel with a lower carbon number is used. In addition, gasoline and other types of higher hydrocarbon-based fuel require higher reforming temperatures in comparison with methanol or the like, and any increase in the temperature of the reforming reaction increases the activity of unwanted reactions involving carbon monoxide, methanol, and the like in the gas phase. Consequently, any attempt to conduct a reforming reaction in an adequate manner is more likely to bring about the opposite result, that is, to promote the formation of carbon monoxide, methane, and other undesirable components.
According to a present invention, there is provided a fuel reforming apparatus for producing a hydrogen-rich gas from a hydrocarbon-based fuel by means of a reforming reaction. The fuel reforming apparatus comprises a fuel decomposition unit and a reforming reactor. The fuel decomposition unit is configured to decompose a first hydrocarbon-based fuel into a second hydrocarbon-based fuel with a lower carbon number. The reforming reactor includes a reforming catalyst for promoting a reforming reaction. The reforming reactor is configured to produce a hydrogen-rich gas from the second hydrocarbon-based fuel by the reforming reaction.
Since the second hydrocarbon-based fuel with a lower carbon number is supplied to the reforming reaction zone, it is possible to reduce formation of soot, which is normally produced because of the high carbon number of the hydrocarbon-based fuel. Such reduced soot formation makes it possible to prevent situations in which the surface of the reforming catalyst is covered with soot, reducing the activity of the reforming reaction. It is also possible to increase the efficiency of the reforming reaction in the reforming reactor. As a result, the reforming reaction can be conducted at a lower temperature, and the reforming unit can be made more compact. Another factor is that the higher the carbon number of the hydrocarbon-based fuel, the more likely it is to adsorb on the surface of the reforming catalyst and to poison the catalyst. Decomposing the hydrocarbon-based fuel before feeding it to the reforming reactor makes it possible to prevent situations in which the activity of the reforming reaction is reduced by the adsorption of the hydrocarbon-based fuel on the catalyst surface.
According to another aspect of the present invention, a fuel reforming apparatus comprises a reforming reactor having a reforming catalyst for promoting the reforming reaction; and means for feeding the hydrocarbon-based fuel to the reforming reactor. The reforming reactor maintains activity of the reforming reaction occurring on a surface of the reforming catalyst while suppressing unwanted gas-phase reactions occurring in the reforming reactor off the surface of the reforming catalyst.
This fuel reforming apparatus suppresses soot formation by reducing the activity of unwanted reactions occurring in the gas phase.
The present invention is further directed to a fuel cell system comprising a fuel cell for generating electromotive force by electrochemical reactions, and a fuel decomposition unit configured to decompose a first hydrocarbon-based fuel into a second hydrocarbon-based fuel with a lower carbon number, wherein the second hydrocarbon-based fuel is fed to the fuel cell to cause the electrochemical reactions.
With this fuel cell apparatus, the undesirable phenomena resulting from the formation of soot in the fuel cell can be prevented because the hydrocarbon-based fuel is decomposed in order to reduce the carbon number before this fuel is fed to the fuel cell. Although the fuel cell is configured such that hydrocarbon-based fuel can be fed directly inside the cell, it is also possible to adopt an arrangement in which a reforming catalyst is further provided on the inside, and hydrogen obtained by reforming the hydrocarbon-based fuel being fed is supplied to the electrochemical reaction zone, or an arrangement in which the hydrocarbon-based fuel being fed is supplied directly to the electrochemical reaction zone.
The present invention is also directed to a method for starting up a fuel cell system, which comprises a fuel cell, and a fuel decomposition unit configured to receive a supply of oxygen and first hydrocarbon-based fuel, and to partially oxidize the first hydrocarbon-based fuel using the oxygen, and to pyrolize the remaining first hydrocarbon-based fuel using oxidation-evolved heat to thereby produce a second hydrocarbon-based fuel with a lower carbon number, where the second hydrocarbon-based fuel is fed to the fuel cell from the fuel decomposition unit. This method is characterized by raising a ratio of an amount of oxygen to an amount of the first hydrocarbon-based fuel fed to the fuel decomposition unit until the fuel cell is heated up to a specified temperature, thereby adequately causing partial oxidation of the first hydrocarbon-based fuel in the fuel decomposition unit and promoting oxidation of hydrogen and carbon monoxide produced by the partial oxidation reaction on an anode-side catalyst inside the fuel cell.
This method allows the requisite warming time to be reduced during the startup of a fuel cell apparatus because the hydrogen and carbon monoxide obtained by the partial oxidation of the first hydrocarbon-based fuel have high oxidation activity and are capable of initiating vigorous oxidation reactions in the fuel cell.
The present invention can be implemented as a variety of embodiments, examples of which include: fuel reforming apparatus, fuel cell systems having the fuel reforming apparatus, methods of operating the apparatus or system, and vehicles having the fuel cell system.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.